The spine comprises a stack of vertebrae with an intervertebral disc between adjacent vertebrae. As shown in FIG. 1, each vertebra 10 includes a vertebral body 12 that supports a bony ring 14. The bony ring 14 consists of laminae 16, spinous process 18, transverse processes 20, superior articular processes 22, and pedicles 24. Together with vertebral body 12, these vertebral components define the spinal canal. The laminae 16 are joined in the midline by the spinous process 18. In the cervical and thoracic region the dural sac 32 contains the spinal cord, which comprises nerves 34 surrounded by cerebrospinal fluid. The fluid-filled sac is therefore compressible. The ligamentum flavum 26 is an elastic yellow ligament connecting the laminae of adjacent vertebrae.
In degenerative conditions of the spine, narrowing of the spinal canal (stenosis) can occur. Lumbar spinal stenosis is often defined as a dural sac cross-sectional area less than 100 mm2 or an anteroposterior (AP) dimension of the canal of less than 10-12 mm for an average male.
The source of most cases of lumbar spinal stenosis is thickening of the ligamentum flavum. Spinal stenosis may also be caused by subluxation, facet joint hypertrophy, osteophyte formation, underdevelopment of spinal canal, spondylosis deformans, degenerative intervertebral discs, degenerative spondylolisthesis, degenerative arthritis, ossification of the vertebral accessory ligaments and the like. A less common cause of spinal stenosis, which usually affects patients with morbid obesity or patients on oral corticosteroids, is excess fat in the epidural space. The excessive epidural fat compresses the dural sac, nerve roots and blood vessels contained therein and resulting in back and leg pain and weakness and numbness of the legs. Spinal stenosis may also affect the cervical and, less commonly, the thoracic spine.
Patients suffering from spinal stenosis are typically first treated with exercise therapy, analgesics and anti-inflammatory medications. These conservative treatment options frequently fail. If symptoms are severe, surgery is required to decompress the canal and nerve roots.
To correct stenosis in the lumbar region, an incision is made in the back and the muscles and supporting structures are stripped away from the spine, exposing the posterior aspect of the vertebral column. The thickened ligamentum flavum is then exposed by removal of the bony arch (lamina) covering the back of the spinal canal (laminectomy). The thickened ligament can then be excised with sharp dissection with a scalpel or punching instruments such as a Kerison punch that is used to remove small chips of tissue. The procedure is performed under general anesthesia. Patients are usually admitted to the hospital for approximately five to seven days depending on the age and overall condition of the patient. Patients usually require between six weeks and three months to recover from the procedure. Many patients need extended therapy at a rehabilitation facility to regain enough mobility to live independently.
Much of the pain and disability after an open laminectomy is due to the tearing and cutting of the back muscles, blood vessels and supporting ligaments and nerves that occurs during the exposure of the spinal column. Also, because these spine stabilizing back muscles and ligaments are stripped and cut off, the spine these patients frequently develop spinal instability post-operatively.
Minimally invasive techniques result in less post-operative pain and faster recovery compared to traditional open surgery. Percutaneous interventional spinal procedures can be performed with local anesthesia, thereby sparing the patient the risks and recovery time required with general anesthesia. Another advantage is that there is less damage to the paraspinal muscles and ligaments with minimally invasive techniques reducing pain and preserving these important stabilizing structures.
Various techniques for minimally invasive treatment of the spine are known. Microdiscectomy is performed by making a small incision in the skin and deep tissues to create a portal to the spine. A microscope is then used to aid in the dissection of the adjacent structures prior to discectomy. The recovery for this procedure is much shorter than traditional open discectomies. Percutaneous discectomy devices with fluoroscopic guidance have been used successfully to treat disorders of the disc but not to treat spinal stenosis or the ligamentum flavum directly. Arthroscopy or direct visualization of the spinal structures using a catheter or optical system have also been proposed to treat disorders of the spine including spinal stenosis however these devices still use miniaturized standard surgical instruments and direct visualization of the spine similar to open surgical procedures. These devices and techniques are limited by the small size of the canal and these operations are difficult to perform and master. Also these procedures are painful and often require general anesthesia. The arthroscopy procedures are time consuming and the fiber optic systems are expensive to purchase and maintain.
In addition, because the nerves of the spine pass through the core of the spine directly in front of the ligamentum flavum, any surgery, regardless of whether is open or percutaneous includes a risk of damage to those nerves.
Hence, it remains desirable to provide a simple method and device for treating spinal stenosis and other spinal disorders without requiring open surgery. It is further desired to provide a system whereby the risk of damage to the thecal sac containing the spinal nerves can be reduced.